Project summary: This proposal will investigate the role of a newly rediscovered posttranslational modification-N-terminal protein arginylation-in cardiovascular development. Prior publications by the PI demonstrate that protein arginylation is critical for cardiovascular development and that knockout of the protein arginylation enzyme ATE1 results in embryonic lethality and severe cardiovascular phenotypes in mice that closely resemble the most commonly occurring congenital heart defects in humans. The proposed research is aimed to gain a general understanding of the role of protein arginylation in cardiovascular development and gain insights into possible mechanisms and ways of treatment of the congenital heart diseases, through the following three specific aims: (1) To test the hypothesis that arginylation regulates cell migration and specification and possibly affects the rates of apopotosis during heart development, using live observations of cultured embryonic cells, immunohistochemistry, insitu hybridization, and microarray profiling;(2) To identify cell lineages responsible for the Ate1 -/- developmental phenotype and to test the hypothesis that this phenotype is due at least in part to changes in cells of the neural creast and endothelial lineages and cardiac myocytes, using conditional mouse ATE1 knockouts;and (3) To identify proteins arginylated in vivo in cardiovascular tissues and to define the possible molecular mechanisms of the Ate1-/- cardiovascular phenotype, using biochemical analysis and mass spectrometry. Taken together, the proposed experiments will allow to identify the specific pathways in cardiovascular development controlled by protein arginylation and to gain insights into the molecular mechanisms of this control at the gene expression and protein level. Relevance to public health: Ate1-/- cardiovascular phenotypes resemble commonly occurring human congenital heart diseases, including ventricular and atrial septal defects (VSD and ASD), persistent truncus artheriosis (PTA), and DiGeorge syndrome. The proposed research is aimed to address the previously unexplored mechanisms of these diseases and provide insights into the new possibilities of their treatment.